[What benefits of cardiac resynchronization therapy in patients with narrow QRS?]

Cardiac resynchronization therapy (CRT) is indicated for patients with electrical dyssynchrony (QRS ≥120 ms). However, mechanical dyssynchrony may also occur in patients with narrow QRS. Echocardiographic criteria of intraventricular dyssynchrony are not univocal; moreover, responsiveness to CRT depends on the criteria utilized for judgment. A unique randomized trial compared CRT with no therapy in patients with heart failure and narrow QRS, but it failed to demonstrate increased peak oxygen consumption with CRT. The results of this study probably depend on the lack of correspondence between activation and contraction delays, at least in ischemic cardiomyopathy.